Genghis2008,
You didn't specify an aircraft, but on the B747-400, if you disengage the autothrottle during cruise mode (CRZ), the reference N1/EPR line will change from a green line displaying the reference N1/EPR (either CRZ or CLB thrust) to a magenta line displaying the N1/EPR required to maintain the FMC cruise mach. It's a nice feature to have.